Abstract
Uniaxial compression at 800°C and 5 kilobars confining pressure of a specimen cored from a single crystal of orthoenstatite [(Mg,Fe)SiO3] produced fine lamellae 100 to 1000 angstroms thick of untwinned clinoenstatite. The two phases are joined along (100) planes and have b and c axes in common. The orientation of the clinoenstatite a axis contradicts several previously suggested transformation mechanisms and reduces the set of possible mechanisms by a factor of 2.